A typical radio access network (RAN) includes a number of base stations each configured to provide coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices, whether or not user operated. In turn, each base station may sit as a node on a core access network that includes entities such as a network controller, switches and/or gateways, and the core network may provide connectivity with one or more external transport networks such as the public switched telephone network (PSTN) and the Internet. With this arrangement, a UE within coverage of the RAN may engage in air interface communication with a base station and may thereby engage in voice calls or other communications on external transport networks.
Such a RAN may operate with a particular air interface protocol, examples of which include, without limitation, Long Term Evolution (LTE) (using orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), and BLUETOOTH. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between base station coverage areas, and other functions.
In accordance with the air interface protocol, each base station may provide wireless service to UEs on one or more carrier frequencies, with the air interface defining various downlink and uplink channels for carrying control signaling and bearer traffic. For instance, on the downlink, the air interface may define channels for carrying reference signals, paging signals, bearer data, and other information from the base station to UEs. And on the uplink, the air interface may define channels for carrying access requests, measurement reports, bearer data, and other information from UEs to the base station.
When a UE initially enters into coverage of such a RAN, the UE may scan for a strongest base-station coverage area in which to operate, and the UE may then engage in signaling to register for service with that base station and the RAN. The UE may then be served by the base station and the RAN and may engage in voice calls or other communications as noted above.
While so served, the UE may also from time to time monitor coverage strength from its serving base station and from other base stations of the RAN, to help ensure that the UE is served with sufficiently strong coverage and perhaps with the strongest available coverage. If the UE's coverage from its serving base station becomes threshold weak and another base station's coverage becomes threshold strong (e.g., threshold stronger than the serving base station's coverage or than a defined level), the UE may then engage in signaling with its serving base station, and the base station and/or one or more other entities may responsively coordinate handover of the UE to the stronger coverage.